1. Field of Invention
The present invention relates to a battery voltage regulating system for controlling an output voltage of an alternating current generator driven by an internal combustion engine and/or a charging voltage for a battery mounted on a motor vehicle.
2. Brief Description of Prior Arts
Various types of voltage regulating systems are known in the art, wherein either a battery voltage or an alternator output voltage is sensed and a field current flowing through a field coil of an alternator is cut off when the sensed voltage exceeds a predetermined value, to thereby maintain the battery voltage at a constant desired value.
The feedback voltage (battery voltage or alternator output voltage) includes generally a relatively large amount of ripple component and a noise component caused by a switching operation of the field current is also included in the feedback voltage. In a conventional voltage regulating system, a delay means is provided to remove an undesirable influence by the above ripple component and/or noise component, a delay time of which is usually some ten microseconds or some hundred microseconds.
In such a system, when a use of an electric load having a large capacity is stopped, a battery voltage is temporarily rapidly increased due to a rapid decrease of consuming current. The feedback voltage is thereby increased to drive a power transistor into a non-conductive state. However, since the delay means is provided in the conventional regulating system, some seconds are required until the power transistor is driven into the non-conductive state, with a result that an excess current flows through the power transistor during that time period causing a breakage of the power transistor.